MRI compatible robot with calibration phantom and phantom

ABSTRACT

A medical robot for use inside an MRI includes a horizontal motion assembly, a vertical motion assembly and a controller. The horizontal motion assembly and the vertical assembly each includes a motion joint, an ultrasonic motor operably connected to the motion joint and an encoder operably connected to the ultrasonic motor. The motor and encoder are positioned proximate to the joint of the respective horizontal motion assembly and vertical motion assembly. Each motor has a cross section positioned in one of the axial and sagittal plane of the MRI. A medical instrument assembly is operably connectable to one of the moving joint of the vertical motion assembly. The controller is operably connected to the horizontal motion joint and the vertical motion joint and it is adapted to be powered off when the magnetic resonance imager is being used to collect images.

CROSS REFERENCE TO RELATED PATENT APPLICATION

This patent application relates to U.S. Provisional Patent ApplicationSer. No. 61/129,319 filed on Jun. 18, 2008 entitled MEDICAL ROBOT FORUSE IN A MRI which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to medical robots and in particular medicalrobots for use in a magnetic resonance imaging device.

BACKGROUND OF THE INVENTION

Medical resonance imaging (MRI) devices are well known medical tools andare used extensively for diagnostic purposes. More recently it hasbecome evident that it would be advantageous to provide a device thatcould be used within a close-bore MRI to perform surgery by remotecontrol. Some medical robots have been developed however each has somesignificant limitations. Specifically there have been suggested somemedical robots that use motors that are positioned 1 to 2 meters fromthe isocentre of the MRI (in fact outside the bore) and are actuatedthrough mechanical linkages. Others have suggested remote manualactuation; zone control of MR-compatibility: no magnetic and electriccomponents at less than 100 cm from the isocenter; motor driver andcontroller at 7 m away with shielded cables; motor electronics and powersupply shielded in Farady cage; power to motor driver cut-off duringscanning; and use of all-pneumatics that leads to larger robots. None ofthese robots provides a solution using ultrasonic motors that arepositionable inside the bore near the isocentre of the MRI.

It will be appreciated by those skilled in the art that there is a needfor reliable robots that can be used in an MRI. Further it would beadvantageous to provide a medical robot with a method of calibrationthat is easy to use. Further it would be advantageous to provide aphantom that can mimic certain anatomical features that can be used forcalibrating the robot, training surgeons and other tasks associated withthe use of a robot in an MRI. It would be advantageous to provide adevice that wherein a portion of it may be visible on an MR image. Itwould also be advantageous to provide a method of determining the besttrajectory for a needle. In addition it would be useful to provide aplatform for use in an MRI that includes a patient receiving portion anda medical robot is adapted to be attached thereto.

SUMMARY OF THE INVENTION

In one aspect of the invention there is a medical robot for use inside amagnetic resonance imager having an axial plane defined by a verticalaxis and a sagittal plane defined by the lateral axis. The medical robotis connectable to a medical instrument assembly. The medical robotincludes a horizontal motion assembly, a vertical motion assembly and acontroller. The horizontal motion assembly includes a motion joint, anultrasonic motor operably connected to the motion joint and an encoderoperably connected to the ultrasonic motor. The ultrasonic motor and theencoder are positioned proximate to the joint. The motor has a crosssection positioned in one of the axial and sagittal plane. The verticalmotion assembly is operably connected to the horizontal motion assembly.The vertical motion assembly includes a motion joint, an ultrasonicmotor operably connected to the motion joint and an encoder operablyconnected to the ultrasonic motor. The ultrasonic motor and the encoderare positioned proximate to the joint. The medical instrument assemblyis operably connectable to one of the moving joint of the verticalmotion assembly and the motion joint of the horizontal motion assembly.The motor has a cross section positioned in one of the axial andsagittal plane. The controller is operably connected to the horizontalmotion joint and the vertical motion joint. The controller is adapted tobe powered off when the magnetic resonance imager is being used tocollect images.

In another aspect of the invention there is a phantom for use inassociation with a magnetic resonance imager. The phantom includes aphantom organ at risk made of a first predetermined material; a phantomtreatable portion made of a second predetermined material different fromthe first predetermined material and differentiable from the firstpredetermined material in a magnetic resonance image; and a phantomsurrounding structure of a third predetermined material and the thirdpredetermined material is different from the first and secondpredetermined material and differentiable from the first and secondpredetermined material in a magnetic resonance image.

In a further aspect of the invention there is a calibration phantom foruse in association with a medical instrument. The calibration phantomincludes a housing that is attachable to a predetermined location on themedical instrument; and at least one channel capable of being visible ina magnetic resonance image, the channel being at a predeterminedlocation to a point of interest in the medical instrument.

In a further aspect of the invention a platform for use in associationwith a medical robot includes a platform having a robot guide adapted toreceive the medical robot; and a patient receiving portion adapted toadjustably position a patient thereon.

In another aspect of the invention there is provided a medicalinstrument comprising a laser fiber having a surrounding channel filledwith a mixture of water and magnetic resonance imager visible fluid.

In another aspect of the invention there is provided a method todetermine the needle trajectory comprising the steps of: providingimages of a predetermined area; determining the location of an irregularzone on the images; calculating a planned target volume from thelocation of the irregular zone; calculating the treatment zone wherebythe treatment zone covers the planned target volume; determining thestarting needle position within a predetermined range; and calculatingthe needle trajectory from the starting needle position to the plannedtarget zone.

Further features of the invention will be described or will becomeapparent in the course of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is a perspective view of the medical robot of the presentinvention having a medical instrument assembly positioned thereon;

FIG. 2 is a blown apart perspective view of the medical robot andmedical instrument assembly of FIG. 1;

FIG. 3 is a perspective view of the horizontal and vertical linearmotion portions of the medical robot;

FIG. 4 is a side view of the pan tilt and rotational portions of themedical robot;

FIG. 5 is a perspective view of the pan tilt and rotational portions ofthe medical robot;

FIG. 6 is a perspective view of the medical instrument assembly ortrocar that is attachable to the medical robot of the present invention;

FIG. 7 is a top view of the medical instrument assembly of FIG. 6;

FIG. 8 is a side view of the medical instrument assembly of FIGS. 6 and7;

FIG. 9 is a perspective view of the medical robot of the presentinvention with the medical instrument assembly ready to be attachedthereto;

FIG. 10 is a front view of the medical robot with the medical instrumentassembly attached thereto;

FIG. 11 is a side view of the medical robot with the medical instrumentassembly attached thereto;

FIG. 12 is a perspective view of the medical robot with the medicalinstrument assembly attached thereto shown between a person's legs;

FIG. 13 is a perspective view of the medical robot with the medicalinstrument assembly attached thereto shown position proximate to aperson who is positioned on their side;

FIG. 14 is a perspective view of an alternate embodiment of a medicalrobot of the present invention having a medical instrument assemblypositioned thereon;

FIG. 15 is a partially blown apart perspective view of the medical robotand medical instrument assembly of FIG. 14;

FIG. 16 is a perspective view of the horizontal and vertical linearmotion portions of the medical robot of the medical robot of FIG. 14;

FIG. 17 is a side view of the pan tilt and rotational portions of themedical robot of the medical robot and medical instrument assembly ofFIG. 14;

FIG. 18 is a perspective view of the pan tilt and rotational portions ofthe medical robot of the medical robot of the medical robot and medicalinstrument assembly of FIG. 14;

FIG. 19 is a perspective view of an alternate embodiment of the medicalinstrument assembly or trocar that is attachable to the medical robot ofthe present invention;

FIG. 20 is a top view of the medical instrument assembly of FIG. 19;

FIG. 21 is a side view of the medical instrument assembly of FIG. 19;

FIG. 22 is a perspective view of the medical robot of the medical robotof the medical robot of FIG. 14 with the medical instrument assemblyready to be attached thereto;

FIG. 23 is a front view of the medical robot with the medical instrumentassembly attached thereto of the medical robot of the medical robot andmedical instrument assembly of FIG. 14;

FIG. 24 is a side view of the medical robot with the medical instrumentassembly attached thereto of the medical robot of the medical robot andmedical instrument assembly of FIG. 14;

FIG. 25 is a perspective view of a platform that provides support for apatient and having the medical robot of the present invention attachedthereto;

FIG. 26 is a side view of the platform of FIG. 25 with the medical robotof the present invention attached thereto;

FIG. 27 is a perspective view similar to that shown in FIG. 25 butshowing the lower portion of a person positioned thereon;

FIG. 28 is a schematic diagram of the control system of the medicalrobot of the present invention;

FIG. 29 is a circuit diagram to transform the digital signal of the RCMinto an analog signal for the driver;

FIG. 30 is a circuit diagram of the motion control system;

FIG. 31 is a circuit diagram of another motion control system; and

FIG. 32 is a block diagram of the motion control of each joint in themedical robot and medical instrument assembly;

FIG. 33 is a schematic diagram of the calibration phantom for use inassociation with a medical instrument assembly with a) showing a frontview, b) showing a side view and c) showing a back view;

FIG. 34 is a perspective view of an embodiment of the calibrationphantom of FIG. 33;

FIG. 35 is a top view of the calibration phantom of FIG. 34;

FIG. 36 is a side view of the calibration phantom of FIG. 34;

FIG. 37 is a back view of the calibration phantom of FIG. 34;

FIG. 38 is a schematic diagram similar to that shown in FIG. 33 a) butshowing the imaginary lines in the calculations;

FIG. 39 is a magnetic resonance image of the calibration phantom of FIG.34;

FIG. 40 is a schematic diagram of a front view of an alternateembodiment of the calibration phantom for use in association with amedical instrument assembly;

FIG. 41 is a front view of a prostate phantom for use in a magneticresonance imager;

FIG. 42 is a perspective view of the prostate phantom of FIG. 41;

FIG. 43 is a magnetic resonance image of the prostate phantom of FIG.41;

FIG. 44 is a schematic diagram of treatment parameters needed todescribe optimal needle trajectory;

FIG. 45 is a schematic diagram of limits to needle trajectory;

FIG. 46 is an alternate schematic diagram of limits to needle trajectoryand showing two zones of interference;

FIG. 47 is a schematic showing the optimal needle trajectory andposition of the treatment zone;

FIG. 48 is a graph showing needle position optimization for differentweighting factors;

FIG. 49 is an enlarged cross sectional view of the laser applicator ofan embodiment of the medical instrument.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to performing medical procedures remotelyusing a robot under the guidance of magnetic resonance imaging (MRI).One function of the robot is to deliver one or more medical device to alocation within the body as selected based on magnetic resonance (MR)images of the body. The MR images are also used to monitor theintervention and the therapy provided in real-time. The robotic deviceis MRI compatible whilst inside the MRI scanner.

In one application, the robotic device is used for tissue ablation. Inthis application, the objective is to destroy a particular region oftissue that may contain a certain size and type of cancerous tumorthrough either heating or cooling. In the present context, the robotwill deliver a heating or cooling device to the MRI-specified location.Heating or cooling will then destroy the tissue in the targeted region.In this application, the temperature change in tissue is monitored asthe heating/cooling is being delivered. The temperature change ismonitored to determine that a sufficient temperature change is achievedto destroy the targeted tissue, as well as to ensure that excesstemperature change (and therefore damage) does not occur in non-targeted(i.e. healthy) tissue. A method of monitoring the temperature change isoutlined in more detail below.

Referring to FIG. 1, the medical robot of the present invention is showngenerally at 10. The medical robot 10 has a medical instrument assemblyor trocar 12 attached thereto. The combined medical robot 10 and medicalinstrument assembly 12 is a six degree of freedom robot which is used toautomatically locate (orientation and position) the tip of the trocarneedle 14 at a selected location near the patient before manuallycontrolled penetration. By way of example, when medical robot 10 is usedfor prostate surgery the tip of the trocar needle 14 is located near theperineum before manually controlled penetration. It will be appreciatedthat penetration may also be automatic. The combined medical robot 10and medical instrument 12 has three linear motion joints and threerotational joints, described in more detail below. As shown by thearrows in FIG. 1, the three linear joints effect horizontal translation16, vertical translation 18 and needle penetration or insertion 20 andthe three rotational joints effect pan 22, tilt 24 and roll 26.

Medical robot 10 has two separate linear motion joints to implementhorizontal 16 and vertical translations 18, respectively. FIG. 3 showsthe structure of the robot base 28 that includes joints to translate themotion horizontally and vertically. The horizontal motion joint consistsof a horizontal ultrasonic motor 30 (preferably USR30-E3N) with ahorizontal encoder 32 a pair of spur gears 34, a horizontal acme leadscrew and nut 36, a pair of horizontal linear guides 36 and a horizontalmoving plate (shown in FIG. 2) 31. The lead screw 35 unit is equippedwith ceramic ball bearings. The actuators are ultrasonic motors thatbeing retentive can lock the joint into position so that no motor brakesare needed. As can been seen the figures horizontal ultrasonic motor 30and horizontal encoder 32 are positioned proximate to the horizontalmotion assembly including the spur gears 34, the horizontal acme leadscrew and nut 35 and the horizontal linear guides 36.

The vertical motion joint consists of a vertical ultrasonic motor 40(preferably USR60-E3N) with a vertical encoder 41, a timing belt and apair of pulleys (not shown), a pair of vertical linear guides 37, avertical acme lead screw and nut 38, and a vertical moving plate 39. Ascan be seen in the figures the vertical ultrasonic motor 40 and verticalencoder 41 are positioned proximate to vertical motion assemblyincluding the timing belt, pulleys, vertical linear guides 37, andvertical acme lead screw and nut 38. All the parts in base 28 includingthe horizontal motion joint and the vertical motion joint are madeeither of Aluminum or plastic. They both have suitable magneticsusceptibility.

The medical robot 10 has three rotation joints: pan (rotation inhorizontal plane), tilt (elevation in vertical plane) and roll(rotation), as best seen in FIGS. 4 and 5. The pan joint unit consistsof a pan shaft assembly 42, a pair of spur gears 43, a timing belt 44and pulleys 46, and a pan ultrasonic motor 48 (preferably USR60-E3N)with a pan encoder 50. The pan ultrasonic motor 48 and pan encoder 50are positioned proximate to the pan assembly including the pan shaftassembly 42, a pair of spur gears, the timing belt 44 and pulleys 46.The tilt and roll joints are composed of two tilt and roll ultrasonicmotors 52 (preferably USR60-E3N) with tilt and roll encoders 54 and abevel gears differential mechanism 56. The transmission is from motors52 to smaller driving bevel gears and then to larger driven bevel gears.When the two driving bevel gears rotate at same speed and samedirection, the tilting movement is realized; and when they rotate atsame speed and reverse direction, the rolling movement is realized.Because the two motors work together, a larger torque output isobtained.

The medical instrument assembly 12 used with the medical robot 10 mayhave a variety functions. In the configuration shown herein the medicalinstrument assembly moves the end point so as to effect insertion orpenetration. Referring to FIGS. 6, 7 and 8, the medical instrumentassembly or trocar module 12 shown herein is for laser ablation. Themain parts of the medical instrument assembly 12 include a “needle” (or“trocar”) tool; pushing and pulling mechanism 62; tapping block 64,tapping cylinder 65, ultrasonic motor 66 (preferably USR60-E3N) withencoder 68 (as seen in FIG. 11), gears 70, guiding block 72 and guidingshaft 74. The pushing and pulling mechanism provide linear motion.

The medical instrument assembly 12 consists of a titanium sheath 75 anda water cooled power laser applicator 76 which protects or cools thelaser diffuser. The pushing and pulling mechanism 62, comprises a leadscrew 82, a pusher with nut 84, a holder 86 of the irrigated power laserapplicator 76 and a sheathe locker 78. The pushing and pulling mechanism62 is adapted to push the needle tools to the target and to retract thesheathe for exposing the laser diffuser tip. It is also adapted to pullthe “needle” tool back after the surgical operation is done. Accordinglythe pushing and pulling mechanism provides linear motion and is thesixth degree of freedom for the medical robot 10. The lead screw 82 isequipped with a pair of ceramic ball bearings. In order to get a highinsertion velocity of the needle tool, a tapping block 64 that ispneumatically driven is added. It will be appreciated by those skilledin the art that the laser diffuser could be replaced with a laserdiffuser with a retractable titanium sheath, a biopsy tool and abrachytherapy tool.

FIGS. 10 and 11 show the medical instrument assembly 12 attached to themedical robot 10 and FIG. 9 shows them just prior to attachment. Thecombined device has six degrees of freedom wherein five degrees offreedom are in the medical robot 10 and one degree of freedom is in themedical instrument assembly 12. In the embodiment shown herein themedical instrument assembly 12 is a trocar device for laser ablation.However, the medical instrument as could also be a device for use withobtaining biopsies or a device for brachytherapy. It will be appreciatedby those skilled in the art that the medical instrument assembly couldalso be designed such that any or all of the pan tilt and roll functionswere part of the medical instrument assembly rather than the medicalrobot.

In order to allow the operator easily and quickly to substitute themedical instrument assemblies 12 without having to make adjustments tothe medical robot 10, simple interfaces between the medical robot 10 andthe medical instrument assembly 12 are provided. A positioning block 90with two pins is attached under the shell 92 of each medical instrumentassembly 12. The shell 92 of the medical instrument assembly 12 isplugged into the hollow of the support block 94 that is coupled with alarge hollow bevel gear 56 on the medical robot 10. The positioningblock 90 is positioned against the rear side of the support block 94 andthen locked in place with a thumb screw 96. Thus the medical instrumentassembly 12 can be quickly mounted on the base unit or medical robot 10.Similarly it can be quickly and easily removed by unlocking with thethumb screw 96 and pulling the medical instrument assembly 12 out of thesupport block 94.

The combined medical robot 10 and medical instrument assembly 12 can bepositioned between a person's legs when the person is lying on theirback as shown in FIG. 12 or positioned below a person's bottom when theperson is positioned on their side as shown in FIG. 13.

An alternate embodiment of the medical robot with an alternateembodiment of a trocar is shown in FIGS. 14 to 24.

The six degree of freedom medical robot 100 is used to automaticallylocate (orientation and position) the medical instrument assembly ortrocar 124. The robot has three linear motion joints (horizontal,vertical and needle penetration) and three rotational joints (pan, tiltand roll). Arrows on FIG. 14 show the horizontal translation 102,vertical translation 104, needle penetration 106, pan 108, tilt 110 androll 112. In addition the robot 100 may include a calibration phantom114. The actuators are ultrasonic motors that being retentive can lockthe needle into position so that no motor brakes are needed. FIG. 14provides a schematic overview and FIG. 15 provides an exploded view ofthe robot 100.

As best seen in FIG. 15, robot 100 includes a horizontal translationunit 116, a vertical translation unit 118, pan unit 120, tilt and rollunit 122, needle penetration unit 124 and a calibration phantom 114.

The robot has two separate linear motion joints to implement horizontaland vertical translations, respectively. FIG. 16 shows the structure ofthe robot base that translates horizontally and vertically. Thehorizontal motion unit 116 includes an ultrasonic motor 126 with anencoder 128 and a linear slide table 130. The vertical motion unit 118consists of an ultrasonic motor 132 with an encoder 134 and a linearslide table 136. The vertical motion unit 118 is attached to thehorizontal motion unit 116. Preferably ultrasonic motors 126 and 132 areUSR60-E3N motors. The parts in horizontal motion unit 116 and verticalmotion unit 118 are made out of the MR compatible materials. Thehorizontal motion unit 116 is attached to a base 137. Base 137 is shapedto accommodate coils used in association with an MR scanner.Specifically base 137 has an arcuate end to accommodate an endorectalcoil (not shown).

The robot has three rotation joints: pan 108 (rotation in horizontalplane), tilt 110 (elevation in vertical plane) and roll 112 (rotation),shown in FIGS. 17, 18 and 20. The pan unit 120 consists of an ultrasonicmotor 138 (preferably USR60-E3N) with encoder 140, a timing belt 142 andpulleys 144 and 146, a pan shaft assembly 148 and a pair of gears 150.The tilt and roll unit 122 is composed of two ultrasonic motors 152(preferably USR30-E3N) with encoders 154, two worm gear reducers 156 anda bevel gears differential mechanism 158. The transmission is frommotors 152 to worm gear reducer 156, then to smaller driving bevel gears(not shown) and then to larger driven bevel gears 160. When the twodriving bevel gears rotate at same speed and same direction, the tiltingmovement is realized; and when they rotate at same speed and reversedirection, the rolling movement is realized. Because the two motors worktogether, a larger torque output is obtained.

The penetration unit or trocar module 124 for laser ablation is shown infigures 17 to 24. The penetration unit 124 consists of the main parts:“needle” (or “trocar”) tool; pushing & pulling mechanism 164; ultrasonicmotor 166 (preferably USR60-E3N) with encoder 168, gears 170, guidingshafts 172, and a calibration phantom 114.

The “needle” tool consists of a titanium (or nitilon) needle 174 and awater cooled power laser applicator 176 which protects or cools thelaser diffuser. The pushing & pulling mechanism 164, which comprises alead screw 178, an insertion unit 180, the holder unit 182 for anirrigated power laser applicator, and a needle locker 184, is adapted topush the needle with the laser applicator tools to the target and the toretract the needle for exposing the laser diffuser tip. And it isadapted to pull the “needle” tool back after the surgical operation isdone. Accordingly the pushing and pulling mechanism provides linearmotion and is the sixth degree of freedom for the medical robot 100. Thelead screw 178 is equipped with a pair of ceramic ball bearings. Thepenetration unit includes a cover 186.

FIG. 22 provides an overview of the medical robot 100 with trocarmodularity such that the robot can be considered as divided into twounits, specifically a five primary DOFs base unit 188; and trocar modulefor laser ablation 124. Other trocar modules could also be used. Forexample trocars for biopsy and brachytherapy could also be used.

In order to allow the operator easily and quickly to substitute thetrocar modules without having to make adjustments to the base unit,simple interfaces between the base unit 188 and the trocar module 124are provided. A positioning block 190 with two pins is attached underthe shell 192 of each trocar module 124 as shown in FIG. 22. By pluggingthe shell 192 of the trocar module 124 into the hollow of the supportblock 194 that is coupled with a large hollow bevel gear 160 on the baseunit 188, and providing the positioning block 190 against the rear sideof the support block 194, then locking with a thumb screw 196 the trocarmodule 124 can be quickly mounted on the base unit. After unlocking withthe thumb screw 196 and being pulled, the trocar module 124 can beeasily removed from the base unit 188.

A platform that provides support for the patient and is adapted to havethe medical robot 100 attached thereto is shown generally at 300 inFIGS. 25 to 27. The platform 300 has a patient receiving portion whichincludes a base plate 302, a haunch support 304, and a pair of legsupport 306, and a robot guide 308 adapted to receive the medical robot.

The haunch support 304 is hingeably attached to the base plate 302 atone end thereof. The haunch support 304 is generally C shaped with twoends which are attached to the pair of leg supports 306. The pair of legsupports are hingeably attached to an adjustable mechanism assembly 310.The adjustable mechanism 310 slides along guide slots 312 at each sidethereof. Reversible wrench 314 moved the adjustable mechanism assemblybackwards and forwards along the base plate 302. In use, the haunchsupport 304 and leg supports can be adjusted so that the pelvis of thepatient is positioned at the appropriate angle.

The medical robot 100 base 137 is shaped to fit over robot guide 308.The robot guide 308 is generally a wedge shape. Knob 318 holds the robot100 in place.

The platform 300 is adapted to be used with a patient transport device(not shown). A plurality of positioners 320 are provided on theunderside of platform 300 and are adapted to engage the patienttransport device.

It will be appreciated by those skilled in the art that the platformdescribed herein is by way of example only and it provides features thatmay be adapted to other types of surgery. Specifically the platformprovides a device for adjustably positioning the patient and moveablysecure a medical robot thereto. The device is designed to be adjustedmanually. The platform is made from MRI compatible materials.

As discussed above, the major function of the robot is to deliver amedical device to a specified location. Further it is important that therobot functions well within the MRI. It was determined that therotational speed of the robot could impact the accuracy of the robotinside the MRI. According to Maxwell's Equations, the faster therotational movement, the greater the electromagnetic interaction betweenthe robot and the main magnetic field of the MRI scanner. Therefore, therotational robotic motion was reduced to reduce the robot-MRIelectromagnetic interaction. Medical robot 100 uses a gearing mechanismto reduce the rotational robotic motion. However, other methods ofachieving the same result are also possible.

Another potential manifestation of the electromagnetic interactionbetween the robot and the MRI environment is the production of eddycurrents. These are electrical currents which are generated inconducting structures by a time-varying magnetic field. The presence ofeddy currents can significantly degrade the quality of MR images.Accordingly, it is preferred that the presence of conducting surfacesand structures is minimized and ideally reduced to zero. Currently basedon equipment that is readily available the source of eddy currents arethe motors and to a lesser extent the encoders. However, it will beappreciated that as ultrasonic motors and encoders are developed whichreduce or eliminate conducting these will be used. In the MRIenvironment, time-varying magnetic fields are present due to bothradiofrequency (RF) waves as well as time-varying linear magnetic fieldgradients. To a good approximation, the RF and gradient processes occurin orthogonal orientations. This implies that if it were possible toorient the motors of the robot in a preferred orientation, the eddycurrents caused by either the gradients or the RF could be minimized.Specifically, if the motors lie in the axial plane, the RF-inducededdy-currents could be minimized, while if the motors lie in thesagittal plane, the gradient-induced eddy currents could be minimized.The x, y and z planes of a MR imager is shown generally at 101 in FIG.14. The axial plane is defined by the vertical or y axis and thesagittal plane is defined by the lateral or Z axis. As can be seen inFIG. 14 medical robot 100 has the cross sections of its motors orientedin the axial and sagittal planes.

In the MRI environment, there are a number of possible sources ofelectromagnetic interaction with the robot. One of the major potentialsources is the local coils that collect the data used to form the MRimages. Typically, these local coils are constructed in a manner thatcreates a close spatial conformation with the anatomy that is beingimaged. For example, when imaging the brain, a local coil that resemblesa helmet is typically used. A method that would minimize theelectromagnetic interaction with the robot and the local coils is tophysically separate the conducting structures of the robot from thelocal coils. In the present invention, the robot motors are positioned aspecified distance (or greater) from the local coils. For example, inthe case of the head coil, the robot motors could be placed at the chestlevel. By way of example only in the embodiment herein the US motors(USR60-E3N) should be placed around 30 cm or more away from the front ofthe robot, and preferably in an axial orientation. The smaller motor(USR60-E3N) could be placed less than 30 cm when they are placed in anaxial orientation.

The MRI scanning operation generates EMI noise that affects the encoder,and this noise causes inaccurate position feedback readings. Inparallel, the ultrasonic motor (U/S) operation generates EMI noise thataffects the clarity of MR images. It was determined that the processor(controller) generates the latter effect, as well as facilitates theformer.

After testing several methods to avoid these effects it has beendetermined that a “power on/off” solution is the best solution.Specifically, it has been determined that turning the controller power(3.3V) on and off, while maintaining the U/S power (24V), and encoderpower (12V) on, suffices in not generating significant EMI, thusacceptable MR images and noiseless encoder readings are produced. Table1 shows the effect the different power sources have on the MR images.Accordingly it is an unexpected result that the device with the lowestpower causes the distortion in the images.

TABLE 1 Scan Image Noise # Power issue Distance ** Cables connectionArtifact (on image) 1 All power * Off 15 cm *** Motors with cables No Noto 20 cm & encoders with cables 2 All power * On 15 cm *** Motors withcables No Significant to 20 cm & encoders with cables RF noise 3  24 Vpower On 15 cm *** Motors with cables No No 3.3 V & 12 V Off to 20 cm &encoders with cables 4 3.3 V power On 15 cm *** Motors with cables No RFnoise  24 V &12 V Off to 20 cm & encoders with cables 5 All power * On15 cm *** Motors without cables No No to 20 cm & encoders withoutcables; all cables are outside the bore 6 All power off  0 cm *** Motorswith cables Yes NO & encoders with cables * Power: DC 24 V, 12 V and 3.3V ** Distance: the distance between the motors on the robot closest toMR scanner isocenter and the scanner isocenter *** Consider all motorswithin_50 cm

In order to store the data of the robot current position when thecontroller power is off, a backup battery is used in the controller tokeep up the current position data in the processor SRAM. A USB devicethat has A/D digital I/O and some relays are included to switch thepower on and off very rapidly.

The control system architecture of the MRI-P is master-slave(decentralized architecture). This helps control accurately the motorposition and speed control.

In contrast in most reported prior art applications of MRI-based U/Smotor control, a centralized architecture is adopted. A decentralizedarchitecture is used herein, with one Rabbit processor RCM3410controlling one motor (FIG. 28). The master controller receives user'scommands, and sends the commands to salve controller via RS485 bus andcustom protocol.

Some time the user may want to stop the motion instantly. But in normalmotion control mode, the controller is busy on checking the positionfeedback synchronously, and cannot receive commands. A separate RCM3410board to communicate with the master controller was included to providethe user with this capability. When the separate controller receives thestop command from the RS485 bus, it sends a digital signal to thetargeted joint controller to instantly stop the motion.

The communication protocol provides communication between master andslave controllers. There are two kinds of frame in the protocol: shortframe and long frame. Long frame is 13 bytes long: it transfers motionparameters from master to slave such as desired speed and targetposition; it also transfers feedback of current position from slave tomaster. Short frame is 6 bytes long; it transfers short commands withoutparameters for fast communication. The main purpose of these protocolsis to speed up the process in order to increase the speed of robotoperation.

The speed of robot operation is a crucial issue in acceptance by themedical community. The need to turn the controller on and off slows downthe operation. There is a need to optimize the process. Note that thisonly relevant in regard to the trocar motor (linear motion) because therobot's other joints are positioned prior to insertion, when the trocaris outside the body.

The motor on/off cycle is divided into the following periods:

UP: time required to reset and initialize the controller after OFF;

ON: time the motor is running (controller is ON);

DOWN: time required to turn OFF the controller;

SCAN: time required to scan, during which the controller is OFF.

The values considered at this time are: UP—0.3 s; ON—depends on therequired average velocity over the cycle; DOWN—0.01 s; SCAN—0.3 s. Themaximum speed of the linear motor is 15.885 mm/s. Thus, for example ifON is 0.39 s (cycle=1 s) the average velocity over the cycle is 6.19mm/s.

The objective here is to minimize the UP and DOWN time by hardware andsoftware design. The ON and SCAN are set by the user. Ideally the totalof UP and DOWN should be minimal to boost up the speed.

Another method to increase the average velocity is to change amechanical part, for example lead of the screw for the penetrationjoint. The lead may be increased by 2 or 4 times. This would increasethe maximum speed 2 to 4 times. But it will also reduce the penetrationforce 2 to 4 times, which is not desirable.

The driver USR60 E3N made by the motor manufacturer provides accuratespeed control. The driver gets the speed feedback form the encoder, andadjusts the output current to the motor to control the motion speed. Thespeed control accuracy is guaranteed by the manufacturer. The speed loopis closed on the driver. The only issue is that the driver of USR60requires an analog signal, but the RCM only outputs digital signals. Acircuit which transforms the PWM output of the RCM into an analog signalto the driver is shown in FIG. 29.

A sensor is used for homing procedure of each joint. During the homingthe sensor is providing a reference position. This signal is highlyrepeatable. When a homing command is generated, the motor is moved in apre-defined direction, while checking the sensor signal. When the signalis detected, it implies that the motor has touched the referenceposition, and the motor stops immediately. Then it is driven to apredefined position, that is the ‘home’.

For pan and tilt joints, they are driven by two interfaced controllers,and only one controller can receive the signal from the sensor, thisreceiving controller will provide the other controller a digital signalsynchronously.

Preferably the control system herein is a closed loop position controlon the slave for each U/S. FIGS. 30 and 31 show the architecture of thismotion control system. The controller sets the speed and motiondirection for the driver. The minimum speed of this type of ultrasoundmotor is 15 rpm (for joint 1 is 30 rpm because it uses a different modelof motor). It means that the motor will move at 15 rpm speed even whenthe speed is set to zero. This characteristic restricts the use ofregular control algorithms such as PID.

The U/S motor is designed to stop as closed to instantly and preciselyas possible. The motion sensor is 500 lines quadrature encoder. Thisimplies that the error (1 count) is 0.18 degree for each joint. Themotion control block diagram is shown in FIG. 32.

When a motion command is received, the controller will send the motiondirection and speed to the driver. Then the controller will check themotor position continuously. When the motor is closed to the commandedposition (within 300 counts), the controller decreases the speed. Whileit moves into the right position, the controller stops the motorimmediately.

In order to use the images generated by the MRI scanner to guide therobot to a specified location, it is necessary to synchronize thecoordinate systems of the robot and the MR scanner. In our system, thisis accomplished by acquiring an MR image while the robot is at aspecific, known location. The position of the robot in the MR images isthen identified. With the MR-derived and robot-known positionsdetermined, the robot and MRI coordinate systems can then besynchronized. To employ this method, one major challenge that must beaddressed is how best to identify the robot position in the MR images.In the present invention, three alternative methods for accomplishingthis task are outlined below:

-   -   A needle is advanced by the robot to some known position inside        an MR-visible object. The MR-visible object could be the human        body, or some external test object (e.g. gel phantom). When        placed in the MR-visible object, the needle will appear dark. In        this manner, the position of the needle tip can then be        visualized on an MR image.    -   A calibration phantom is used that can indirectly provide the        position of a needle tip on MR images. The calibration phantom        consists of 4 water channels (see FIG. 33). The needle lies in        the exact middle of all four channels. The needle position is        determined as follows: First, the location of each water filled        channel is determined on an MR image. Second, the centre point        of the four needles is calculated from these locations (see FIG.        38). This procedure localizes the needle tip in two planes. A        similar procedure is performed in an orthogonal plane to        localize the needle position in the third dimension. FIG. 39 is        an MR image of a prototype calibration phantom. In future robot        designs, the calibration phantom may be incorporated directly        into the robot itself.    -   The needle may be filled and/or surrounded by water (or        contrast-agent-doped water). In this manner, the needle can be        visualized on MR images.

More specifically, an embodiment of calibration phantom 114 including aschematic representation of the front a) side b) and back c) is shown inFIG. 33. The calibration phantom 114 is also shown in FIGS. 34 to 37.The calibration phantom 114 includes four water filled channels 200 anda filling port 202. The needle holder 204 is in the centre of the fourchannels 200. The calibration phantom includes a housing 201 that isattachable to a medical instrument. It will be appreciated by thoseskilled in the art that the calibration phantom 114 is shown attached toa specific trocar. However, it could be adapted to be used to locate anytype of medical instrument wherein the channels are at a predeterminedlocation to a point of interest in the particular medical instrument. Inthe example shown herein the point of the interest is the needle tip202.

The calibration phantom 114 includes water-filled tubes 200 oriented ina manner such that a line drawn between the two will go through theneedle tip 202 (see FIG. 38).

In calculating the location of the needle tip 202 it is assumed thatthere is effectively no error in the “true” position of the water-filledtubes. On the MR image, the position of the needle tip is calculated asfollows:

-   -   1) The (x,y) position of a water-filled tube, together with the        corresponding tube on the opposite side will be measured. The        mid-point along a line drawn between these two tubes will        correspond to the needle tip:

$\left( {x_{tip}^{1},y_{tip}^{1}} \right) = \left( {{\frac{1}{2}\left\lbrack {x_{a}^{1} + x_{b}^{1}} \right\rbrack},{\frac{1}{2}\left\lbrack {y_{a}^{1} + y_{b}^{1}} \right\rbrack}} \right)$

-   -   -   The uncertainty in position of all measured points (x_(a) ¹,            x_(b) ¹, y_(a) ¹, y_(b) ¹) will be the image resolution (δ).            This uncertainty can be considered as the standard deviation            of a distribution about the true position of each point (the            specific form of the distribution does not matter for this            derivation, though it could be safely assumed to be Gaussian            if necessary). It is assumed that the uncertainty in            position of one measurement is uncorrelated with any other            measurement (the validity of this assumption will be            discussed later). Under these assumptions, it follows            trivially from basic statistics that the standard deviation            of x_(tip) ¹ and y_(tip) ¹ is δ/√{square root over (2)}.

    -   2) Step #1 is repeated for all remaining n/2 pairs of tubes. The        uncertainty in the estimate of needle tip position from each of        these measurement is

$\left( {x_{tip}^{i},{y_{tip}^{i};{i = {1\mspace{14mu}\ldots\mspace{14mu}\frac{n}{2}}}}} \right)$is δ/√{square root over (2)}, as in step #1.

-   -   3) The average of all estimates of needle tip position is taken:

$\left( {x_{tip}^{av},y_{tip}^{av}} \right) = {\frac{1}{n/2}{\sum\limits_{i = 1}^{n/2}\;\left( {x_{tip}^{i},y_{tip}^{i}} \right)}}$

-   -   -   Since the standard deviation of each position is (x_(tip)            ^(i),y_(tip) ^(i)) is δ/√{square root over (2)} and with the            assumption that all of the (x_(tip) ^(i),y_(tip) ^(i)) are            uncorrelated, the standard deviation of (x_(tip)            ^(av),y_(tip) ^(av)) is therefore:

$\frac{\delta/\sqrt{2}}{\sqrt{n/2}} = \frac{\delta}{\sqrt{n}}$

This derivation is predicated on the assumption that all measurements ofposition are uncorrelated. This is likely true for all situations exceptthe degenerate case where the water-filled tubes are aligned at 0 or 90degrees. In this case, the tube position and the imaging grid will bealigned with each other, and the measurements will be correlated foreither the x or y position. The solution to this is simply to avoidplacing the water filled tubes at the 0 or 90 degrees position.

Alternatively the calibration phantom 114 may include an annular ring ofwater 206 and the needle tip 208 is calculated at the centre of thecircle as shown in FIG. 40.

Referring to FIG. 49 a laser applicator is shown generally at 600. Laserapplicator 600 may be used in association medical instrument 12 shown inFIG. 1 and in detail in FIG. 6 to 8 or medical instrument 124 shown inFIG. 14 in detail in FIGS. 19 to 21. Laser applicator 600 includes alaser fiber 602 surrounded by an inner catheter 604 and an outercatheter 606. Inner catheter 604 is in flow communication with outercatheter 606. Outer catheter 606 has an outlet port 608 and innercatheter 604 has an inlet port 610. Catheters 604 and 606 has a mixtureof water and an MRI visible fluid circulating therethrough. Preferablythe MRI visible fluid is Gd (gadolinium) and the fluid includes between10% and 1% Gd.

For some applications, it may be desirable for the robot and the MRscanner to exchange information and/or data with each other. The presentinvention proposes several methods of achieving this communication:

-   -   Images and/or data may be transferred between the robot and MR        scanner via FTP.    -   Images may be transferred between the robot and the MR scanner        via DICOM push/pull protocols    -   Images and/or data may be transferred between the robot and MR        scanner through the MR scanner's built-in real-time protocol        (RTP).    -   Images and/or data may be transferred between the robot and MR        scanner through a BiT3 device.

One particular application where robot/MRI communication may beessential is in real-time robotic visualization. In this application, MRdata acquisition and robotic usage occur simultaneously. However, incases where the electromagnetic coupling cannot be sufficientlysuppressed, then the activation of the MR scanner and the robot could beinterleaved. In this scenario, robotic usage and MR data acquisition areswitched on and off in rapid succession to simulate real-timefunctionality and the on/off states of the MR scanner and the robot areco-ordinated. This coordination could be achieved by sending signalsback and forth between the MR scanner and robot using one of theaforementioned data communication mechanisms. An additional method ofachieving such communication could be via TTL signals.

Within an MRI imaging exam, a variety of different pulse sequences, andpulse sequence parameters may be used to affect the visualization of theobject being imaged. The specific pulse sequence and parameters used fora particular application are typically chosen to optimize thevisualization of the object. This optimization may include (but notlimited to) maximizing signal-to-noise ratio (SNR), maximizingcontrast-to-noise ratio (CNR), and minimizing artifacts. For the roboticapplication, a gradient echo pulse sequence with a short echo time (TE)was determined to provide a good visualization of the needle. When theneedle and/or fibre was filled with Gadolinium contrast agent, afast-spin-echo (FSE) pulse sequence with a short echo time wasdetermined to provide a good visualization. For visualizing coagulation,three different pulse sequences are used: long-TE FSE, T1-weighted FSE,and short-TR gradient echo.

To monitor temperature in real-time with MRI, several methodologies hadto be developed. First, a technique for converting MRI data intotemperature elevation maps was implemented. This technique utilizes thephase of MRI images. Secondly, a technique for accessing the data inreal-time was developed. In the current implementation, data wasaccessed via FTP. More generally, however, other methods including thoseoutlined above are possible.

An anatomically correct MR compatible phantom suitable for focalinterventions is useful in the design, development, testing and trainingof medical robots for use in an MRI.

The phantom 400 shown herein in FIGS. 41 to 43 is designed to beanatomically correct, MR compatible and contain a part that would allowfocal ablation. Phantom 400 includes a treatable portion 402 which inthe example herein is approximately 5 cc, an anatomically correct“prostate” 404 and a perineum like structure 406 with “rectum” 408.

The treatable portion 402 varies according to focal intervention type.It is made of different shelf gels with different properties. The gelmay be dye green and includes some intralipid fat and proteins that makeit amendable to coagulation using laser energy. Alternatively adifferent gel may be used that makes it amendable to HIFU thermalenergy. For example materials from ATS LAbratories Inc. may be used

In the embodiment herein, the “prostate” 404 is made in a mold. The moldis a simple mold and can be made to any prostate size. The “prostate” ismade from a gelatin that is commercially available in every supermarketwith Gadolinium added to the mixture. The “urethra” 410 of the prostateis made from a Foley catheter.

The perineum like structure 406 is made in a cubical mold with an opentop. The “rectum” 408 is created by using a tube in place while fillingthe mold. The material of the “perineum” is commercially availabledental histomer. Once the lower part of the perineum is created, the“prostate” is placed on top and the mold is filled to encompass theprostate. By way of example Cavex CA37, Cavex CA37 Normal Set andCavexCA 37 Fast Set made by Haarlem CAVEX HOLLAND B.V and which arealginate impression materials for dental use may be used to make theperineum like structure 404.

It will be appreciated by those skilled in the art that the phantomherein 400 is a combination of standard materials but it allows forfocal ablation of predefined volume. The different materials used give adifferent MR signal that ultimately makes for a close approximation ofthe human prostate with a tumour inside. An MR image of the phantomherein is shown in FIG. 43.

Current practice in treating prostate cancer uses trans-perineal needleinsertions, such as brachytherapy, PDT, photothermal, etc., through atemplate that fixes the needle insertion points to a grid of 5 mmspacing and orientation perpendicular to the plate. While this worksreasonably well for treating the whole organ, in focal treatments, suchan arrangement provides poor targeting resolution. Further, the shapeand position of the planned target volume (i.e. the tumour plus somemargin) may require multiple needle insertions even though the plannedtarget volume (PTV) may be small and only require a single needle forcomplete coverage if restrictions on needle position and angle wererelaxed. A manual oblique angle needle insertion device, with sensors toindicate needle track and position may be used for this type of surgery.

To be fully functional, a method is provided to optimize the needletrajectory and its starting position, based on complete treatment of thetumour (or PTV) and avoidance of other critical structure. Therequirements of the method are therefore:

-   -   Complete treatment of the tumour Avoidance of treatment to any        surrounding organs that may be at risk.        The limits of the method are therefore:    -   Extent of trajectory angle as determined by the device.    -   Extent of trajectory angle as determined by any internal bones,        such as the pubic arch.

The above criteria are shown in a 2D representation at 500 in FIG. 44,and will be discussed in detail below.

Trajectory optimization requires determining the x′, the startingcoordinate of the needle and θ, the trajectory angle. For overlap of thetreatment zone, the orientation, θ, and centre of the treatment zone(x_(c), y_(c)) are required. The figure shows several of therequirements noted above. First, the treatment zone 502 fully covers thePTV 504. Secondly, the treatment zone 502 has minimal overlap with theorgan at risk 506, but some overlap is still present. Thirdly, withoutthe pubic arch 508, the motion of the needle is limited by the width ofthe device (x_(o) to x_(end)). Both of these limits, and the depth ofthe target, restrict the trajectory angle, θ. If the pubic arch 508 ispresent, then the trajectory angle is further restricted. Details ofresolving this are given below.

In FIG. 44, the treatment zone 502 for a fiber is an ellipse, with thefiber axis following along the long axis of the treatment zone. The PTV(or tumour) 504 is completely covered by the treatment zone of the lightdelivery fiber, which is the desired outcome. The organ at risk (OAR)506 is also partly covered by the treatment zone, an undesirable effect.Optimization of the trajectory requires maximal overall of the treatmentzone with the PTV 504, and minimal overlap with the OAR 506. Tocalculate the optimization, the photothermal dose delivered to thepatient, D_(P) and the resulting tissue response is considered. As afirst approximation, the tissue response is considered as a simplethreshold effect. In this case, treatment response, defined as E_(k) forvoxel k, can be described as:

$\begin{matrix}{{E_{k} = \begin{Bmatrix}{0;} & {D_{P} < D_{Threshold}} \\{1;} & {D_{P} \geq D_{Threshold}}\end{Bmatrix}},} & 1\end{matrix}$where D_(Threshold) is the minimum photothermal dose required to producea coagulative response. More sophisticated models that include the fullthermal dose can be used here, but our current observations indicateessentially a threshold effect. In these equations it is assumed thatthe threshold dose is the same for all tissue.

Referring to FIG. 48, to optimize the treatment delivery, the effectshould be maximized for treatment of the PTV and minimized for any othertissues. In this case only a single OAR is considered. This can besummarized by the optimization/minimization of the following generalizedcost function:

$\begin{matrix}{{F = {{w_{j}^{PTV}\left( {M - {\sum\limits_{j = 1}^{M}\; E_{j}}} \right)} + {\sum\limits_{i = 1}^{N}\;{w_{j}^{ORV}E_{i}}}}},.} & 2\end{matrix}$Here, the PTV and OAR have volumes of M and N voxels each. The first 2terms describe the overlap of the PTV and the treatment effect. As moreof the PTV receives a treatment above the threshold dose, the summationterm increases, and the difference with the total number of voxelsapproaches 0. The third term represents the overlap of the OAR with thetreatment zone. As more of the OAR receives a treatment above thethreshold dose, this term increases in magnitude.

The effect of the dose delivered to each site, j, is weighted in theabove equation using the “importance factors”, w_(j). In the instance ofthe OARs, the magnitude is proportional to the clinical impact ofdamage. If clinical outcome is not impacted, either by function orcosmetics, treatment of the OAR is “not important”, and has no effect onthe optimization of the treatment plan, and the dose to the OAR can behigher than the threshold dose. Conversely, if there is a clinicalimpact, the clinician may need to weigh the importance of possiblyundertreating the PTV (D_(P)<D_(T)) with possibly overtreating the OAR(D_(O)>D_(T)). The relative magnitudes of the importance factors guidethis balance.

Consider an example with 3 OAR's, the prostate, rectum and erectilenerves. Treatment of the normal prostate has minimal clinical effect,and so the weighting terms are set to 0 for the focal therapy. Treatmentof the rectum would lead to significant clinical morbidity, and so theweighting term is set high. Treatment of the erectile nerves may dependon the patient. If it is crucial for the patient to preserve erectilefunction, than the weighting can be set high. If this is less importantto the patient (possibly due to current conditions that limit his sexualfunction), then the weightings can be lower.

Optimization of the treatment requires minimizing the cost functionusing the centre (x_(c), y_(c)) and orientation, θ, of the treatmentzone as adjustable parameters. However, these parameters will be limitedby the physical limitations placed on the needle insertion, i.e.trans-perineal needle insertion using a mechanical device with sizelimits.

The brachytherapy device has a travel limit of 10 cm, which consequentlyrestricts the travel of the needle holder and hence the trajectory intothe prostate. FIG. 45 shows the 2D limits to the needle trajectory basedon the physical limits of the device. The same considerations apply inthe z-coordinate.

θ_(min), and θ_(max) represent the minimum and maximum angle ofinsertion, while θ is the optimal trajectory angle. These angles aredefined not only by the travel limits of the device, but also by theposition of the PTV. In this instance the centre of the PTV is taken asthe target position, since this will be close to the centre of thetreatment zone. Based on this, the optimal trajectory is given by:θ_(min)=tan⁻¹((x _(c) −x′)/y _(c)),  3.The limits to the trajectory orientation are:θ_(min)=tan⁻¹((x _(c) −x ₀)/y _(c)),  3a.θ_(max)=tan⁻¹((x _(c) −x _(end))/y _(c))  3b.

If the pubic arch interferes with the optimal trajectory, a similarapproach to that given above can be used to define the limits. However,the limits need to be redefined based on the limits posed by the pubicarch.

The pubic arch can be considered as 2 separate left and right zones ofinterference as shown in FIG. 46. For each region, the appropriateextent of the pubic arch along the x-coordinate needs to be found suchthat the needle trajectory does not overlap with the pubic arch.

To find these limits, the centre (x_(pc)) and limits (x_(pm), x_(pn)) ofthe each region must first be measured along the x coordinate. A linecan be drawn from the PTV centre of the mass to the outer limit of thepubic arch, (x_(pm), y_(pm)), and then further extended to needlestarting position. This line will determine of the outer limits, x₀ andx_(end). The procedure is then repeated for the other side. Thefollowing algorithm is used to find the limits:

xpc = mean(xp); % centre of pubic arch along x coordinate [xpm,imxp] =max(xp); [xpn,inxp] = min(xp); % max and min % starting conditionsmatching the device limits x_0 = 0; x_end = 40; if xpm > xpc xp_t =xpm + 1; % provides some buffer in the trajectory yp_t = ypm; % matchingy coordinate x_0 = (xp_t − xc)*yc/(yc − yp_t) + xc; % ratio of triangleselse xp_t = xpn − 1; yp_t = ypn; x_end = (xp_t − xc)*yc/(yc − yp_t) +xc; endThe algorithm is repeated for the other pubic region using the newlimits for x₀ and x_(end).

Initial tests of the optimization procedure were performed using MatLAB,using (x_(c), y_(c)) and θ as adjustable parameters. The MatLABoptimization routines, however, were very insensitive to the orientationand hence were poor in finding optimal solutions. A different approachwas used based on the starting needle position and the centre of thePTV. Since i) the mechanical device has a limited resolution and ii) therequired resolution is approximately ±1 mm, the cost function can becalculated for the complete range of initial starting positions. Therange of starting positions can be set by limits discussed above due tothe pubic arch or other anatomical features. The iteration procedurethen becomes.

Calculate (x_(c), y_(c)) for PTV, based on centre of mass

For x′=x_(o) to x_(end)

-   -   Calculate F for treatment zone calculated using x′, (x_(c),        y_(c))    -   Keeping θ fixed, minimize F by varying (x_(c), y_(c))    -   If F_(k)<F_(k-1) return, else store (x_(c), y_(c)) and continue

Find x′ with minimal F, and calculate trajectory based on x′, and(x_(c), y_(c))

Another approach would use standard optimization routines and minimizethe cost function by simultaneously adjusting (x_(c), y_(c)) and θ, withlimits determined by the pubic arch.

A 2D example of the needle trajectory optimization is shown in FIG. 47.Here the planned target volume is not perpendicular to the needletemplate plane (defined by the x-axis). An organ at risk lies adjacentto the PTV. The figure on the right shows the cost-function value usingdifferent weighting values for the OAR (w_(OAR) in Eqn. 2). Whenw^(OAR)=0, as with the blue line in the FIG. 4 b, the cost function onlyreaches 0 when the target zone completely overlaps the PTV. This onlyoccurs when the starting needle position is at 16-17 mm, with the needleaimed at the centre of the PTV. Adding some weighting to the OARincreases the cost function, and slightly changes the optimal needletrajectory. However, in this case the cost function never completelygoes to 0 since some of the OAR falls within the Treatment Zone.

The above example demonstrates the process in 2 dimensions. Extension to3 dimensions requires optimization of not just x′ and θ, but instead(x′, y′) and (θ, φ)

A needle tracking optimization method has been developed that includesmaximizing total dose to the planned target volume while minimizing thedose to any surrounding critical organs and to avoid any objects thatare potentially in the path of the needle. The current model uses asimple method of accounting for the treatment response. Moresophisticated models that incorporate the thermal dose can also beapplied. Further, avoidance of the critical structures can alsoincorporate dose models that account for clinical morbidity due to thecreation of hot spots within the organ. For instance, in avoiding therectum, the plan may lead to little dose in the organ as a whole, but ifthe entire dose is at a single hot spot, then it can lead to an adverseevent.

It will be appreciated by those skilled in the art that the abovediscussion may be generalized as a method to determine the needletrajectory comprising the steps of: providing images of a predeterminedarea; determining the location of an irregular zone on the images;calculating a planned target volume from the location of the irregularzone; calculating the treatment zone whereby the treatment zone coversthe planned target volume; determining the starting needle positionwithin a predetermined range; and calculating the needle trajectory fromthe starting needle position to the planned target zone. This can beenhanced by including the steps of determining the location of at leastone zone at risk on the images; and determining the location of at leastone avoidance zone from images and wherein calculating the needletrajectory includes factors to avoid the avoidance zones. In mostinstances the zone at risk is an organ, the irregular zone is a tumorand each avoidance zone is a bone. Preferably the images are magneticresonance images. Further, the method may include the steps ofdetermining from the images a temperature evaluation image anddetermining from the temperature evaluation image if an actual treatmentzone equals the planned treatment zone.

Generally speaking, the systems described herein are directed to medicalrobots and medical instrument assemblies. As required, embodiments ofthe present invention are disclosed herein. However, the disclosedembodiments are merely exemplary, and it should be understood that theinvention may be embodied in many various and alternative forms. TheFigures are not to scale and some features may be exaggerated orminimized to show details of particular elements while related elementsmay have been eliminated to prevent obscuring novel aspects. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting but merely as a basis for the claims and as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention. For purposes of teaching and notlimitation, the illustrated embodiments are directed to medical robotsand medical instrument assemblies.

As used herein, the terms “comprises” and “comprising” are to construedas being inclusive and opened rather than exclusive. Specifically, whenused in this specification including the claims, the terms “comprises”and “comprising” and variations thereof mean that the specifiedfeatures, steps or components are included. The terms are not to beinterpreted to exclude the presence of other features, steps orcomponents.

1. A medical robot for use inside a magnetic resonance imager having anaxial plane defined by a vertical axis and a sagittal plane defined bythe lateral axis, the medical robot being connectable to a medicalinstrument assembly comprising: a horizontal motion assembly including ahorizontal motion joint, a horizontal ultrasonic motor operablyconnected to said horizontal motion joint and a horizontal encoderoperably connected to said horizontal ultrasonic motor, wherein saidhorizontal ultrasonic motor and said horizontal encoder are positionedproximate to said horizontal motion joint; a vertical motion assemblyoperably connected to the horizontal motion assembly, the verticalmotion assembly including a vertical motion joint, a vertical ultrasonicmotor operably connected to said vertical motion joint and a verticalencoder operably connected to said vertical ultrasonic motor, whereinsaid vertical ultrasonic motor and said vertical encoder are positionedproximate to said vertical motion joint and the medical instrumentassembly is operably connectable to one of said vertical motion jointand said horizontal motion joint; and a controller operably connected tothe horizontal motion joint and the vertical motion joint; wherein theultrasonic motors each has a corresponding cross section positioned in aplane selected from the group consisting of the sagittal plane and axialplane of the magnetic resonance imager.
 2. The medical robot as claimedin claim 1 further including a pan assembly operably connected to one ofthe vertical motion assembly and the horizontal motion assembly and themedical instrument assembly is operably connectable to one of the panassembly, the vertical motion assembly and the horizontal motionassembly, the pan assembly including a pan joint, a pan ultrasonic motoroperably connected to the pan joint and a pan encoder operably connectedto the pan ultrasonic motor, the pan ultrasonic motor and pan encoderare positioned proximate to the pan joint, the pan ultrasonic motor ispositioned in one of the axial and sagittal plane and the pan assemblyis operably connected to the controller.
 3. The medical robot as claimedin claim 2 further including a tilt assembly operably connected to oneof the pan assembly, the vertical motion assembly and the horizontalmotion assembly and the medical instrument assembly is operablyconnectable to one of the tilt assembly, the pan assembly, the verticalmotion assembly and the horizontal motion assembly, the tilt assemblyincluding a tilt joint, a tilt ultrasonic motor operably connected tothe tilt joint and a tilt encoder operably connected to the tiltultrasonic motor, the tilt ultrasonic motor and the tilt ultrasonicmotor are positioned proximate to the tilt joint, said tilt ultrasonicmotor is positioned in one of the axial and sagittal plane and the tiltassembly is operably connected to the controller.
 4. The medical robotas claimed in claim 3 further including a roll assembly operablyconnected to one of the tilt assembly, the pan assembly, the verticalmotion assembly and the horizontal motion assembly and the medicalinstrument assembly is operably connectable to one of the roll assembly,the tilt assembly, the pan assembly, the vertical motion assembly andthe horizontal motion assembly, the roll assembly including a roll jointand a roll ultrasonic motor operably connected to the roll joint and aroll encoder operably connected to the roll ultrasonic motor, the rollultrasonic motor and the roll encoder are positioned proximate to theroll joint, said roll ultrasonic motor is positioned in one of the axialand sagittal plane, and the roll assembly is operably connected to thecontroller.
 5. The medical robot as claimed in claim 4 wherein the tiltassembly and the roll assembly are a combined tilt and roll assembly. 6.The medical robot as claimed in claim 5 wherein the horizontal motionassembly further includes a horizontal lead screw operably connected tothe ultrasonic motor of the horizontal motion assembly, a pair of spurgears operably connected between said horizontal lead screw and ahorizontal plate.
 7. The medical robot as claimed in claim 6 wherein thevertical motion assembly further includes a vertical lead screw operablyconnected to the ultrasonic motor of the vertical motion assembly and atiming belt and pair of pulleys operably connected between said verticallead screw and a vertical plate.
 8. The medical robot as claimed inclaim 7 wherein the pan motion assembly further includes a pan shaftassembly operably connected to the pan ultrasonic motor, a timing beltand pulleys operably connected to the pan shaft assembly and operablyconnectable to the medical instrument assembly.
 9. The medical robot asclaimed in claim 8 wherein the combined tilt and roll assembly furtherincludes a bevel gear differential mechanism operably connected to thetilt ultrasonic motor and the roll ultrasonic motor and the bevel geardifferential mechanism is operably connectable to the medical instrumentassembly.
 10. The medical robot as claimed in claim 9 wherein each ofthe ultrasonic motors is positioned a predetermined distance from alocal coil used in the magnetic resonance imager whereby the positioningthereof reduces electromagnetic interaction with the magnetic resonanceimager.
 11. The medical robot as claimed in claim 10 further includinggears operably connected to at least one of the ultrasonic motors. 12.The medical robot as claimed in claim 11 further including a gearsattached to each of the ultrasonic motors.
 13. The medical robot asclaimed in claim 4 wherein the medical instrument assembly is a trocarand the trocar is operably connected to the controller.
 14. The medicalrobot as claimed in claim 4 wherein the medical instrument assemblyincludes a pushing and pulling mechanism operably connected to anultrasonic motor positioned proximate thereto.
 15. The medical robot asclaimed in claim 14 wherein the pushing and pulling mechanism includes apushing and pulling lead screw operably connected to the ultrasonicmotor, a holder operably connected to the pushing and pulling lead screwand the holder being adapted to hold a laser applicator and furtherincluding a locker operably connected to the lead screw.
 16. The medicalrobot as claimed in claim 15 wherein the medical instrument assemblyfurther includes a pneumatically driven tapping block operably connectedto the pushing and pulling mechanism.
 17. The medical robot as claimedin claim 16 wherein a combination of the medical robot and the medicalinstrument assembly is a six degree of freedom medical robot and theultrasonic motors are adapted to be positionable within the isocentre ofthe medical resonance imager.
 18. The medical robot as claimed in claim15 whereby the controller is rapidly turned on and off interleavedbetween the turning on the magnetic imager, imaging and turning off ofthe magnetic resonance imager, thereby interleaving the imaging withmovement.
 19. The medical robot as claimed in claim 18 whereby theimaging includes imaging sequences whereby the imaging sequences are oneof a gradient echo pulse sequence with a short echo time and afast-spin-echo pulse sequence with a short echo time.
 20. The medicalrobot as claimed in claim 18 whereby the imaging includes imagingsequences whereby the imaging sequences include three different pulsesequences including long-TE FSE, T1-weighted FSE, and short-TR gradientecho.
 21. The medical robot as claimed in claim 14 wherein the medicalinstrument assembly further includes one of a laser diffuser with aretractable titanium sheath, a biopsy tool and a brachytherapy tool. 22.The medical robot as claimed in claim 4 further including a controlsystem operably connected to the controller and remote from and isolatedfrom the controller.
 23. The medical robot as claimed in claim 22wherein the control system is isolated by one of a predetermineddistance and magnetically isolated.
 24. The medical robot as claimed inclaim 4 further including a calibration phantom attached to the medicalinstrument assembly.
 25. The medical robot as claimed in claim 24wherein the calibration phantom includes a housing that is attachable toa predetermined location on the medical instrument, at least one channelformed in the housing capable of being visible in a magnetic resonanceimage, the channel being at a predetermined location to a point ofinterest in the medical instrument.
 26. The medical robot as claimed inclaim 25 wherein the at least one channel is a plurality of channels.27. The medical robot as claimed in claim 26 wherein there are fourchannels.
 28. The medical robot as claimed in claim 25 wherein the atleast one channel is an annular ring.
 29. The medical robot as claimedin claim 25 wherein each channel is filled with a mixture of water andmagnetic resonance imager visible fluid.
 30. The medical robot asclaimed in claim 4 wherein the medical instrument includes a laser fiberhaving a surrounding channel filled with a mixture of water and magneticresonance imager visible fluid.
 31. The medical robot as claimed inclaim 4 further including a platform having a robot guide adapted toreceive the medical robot and a patient receiving portion adapted toadjustably position a patient thereon.
 32. The medical robot as claimedin claim 31 wherein the platform includes a base and the patientreceiving portion includes a haunch support hingeably attached to thebase and a leg support hingeably attached to the haunch support.
 33. Themedical robot as claimed in claim 32 wherein the patient receivingportion further includes an adjustable mechanism assembly operablyconnected to the leg support whereby movement of the adjustablemechanism repositions the haunch support relative to the leg support.34. The medical robot as claimed in claim 33 further including a pair ofguides one on each side of the base and the adjustable mechanismassembly engages the guides and is moveable along the guides.
 35. Themedical robot as claimed in claim 34 wherein the robot is moveable alongthe guides.